1. Field of the Invention
This invention relates to a new process for the synthesis of fullerenes (a family of carbon molecules). More particularly, the invention relates to a process whereby fullerenes are produced by dissociating a carbon halide or a hydrocarbon using a plasma torch.
2. Brief Description of the Prior Art
Until recently, only two forms of carbon were known to exist: graphite and diamond. In graphite the carbon atoms form sheets stacked on top of each other while in diamond, each carbon atom is covalently bonded to four other carbon atoms forming a giant network of small pyramids.
Another form of carbon, the "fullerenes", has lately been successfully synthesized and identified. Basically, fullerenes are hollow molecules made up of curled-up graphitic sheets. These carbon molecules can contain anywhere from 32 to 960 carbon atoms and are all believed to have the structure of geodesic domes. The name "fullerenes" was chosen in honour of Buckminster Fuller who developed the structure of the geodesic dome. The molecules are also called "buckminsterfullerenes" or "buckyballs" for short. The molecules containing 60 carbon atoms (C.sub.60) are considered to be the most important due to their high stability. Molecules containing 70 carbon atoms (C.sub.70) are also highly stable. Hence, "buckyballs" often refer to C.sub.60 and/or C.sub.70. Molecules containing very large numbers of carbon atoms are also called "hyperfullerenes".
In 1985, Robert F. Curl and Richard E. Smalley of Rice University working with Harold W. Kroto of the University of Sussex, found that a new form of carbon, C.sub.60, could be made by vaporizing graphite in helium using a pulsed laser beam. The production rate of fullerenes using this technique is, however, extremely slow (few grams/day).
In May 1990, five years later, Wolfgang Kratschmer and Donald Huffman were the first to observe and positively identify this molecule. At a conference in Germany in early September of 1990, Kratschmer and Huffman announced that they had found a much simpler way to synthesize C.sub.60. They were able to make fullerenes by striking an arc between two graphite electrodes and collecting the soot formed from the vaporized carbon. However, with a production rate of roughly 1 gram/hour, the arc vaporization of graphite is also a very slow process.
Several recent articles describe fullerenes and their uses and potential applications. For example, in the article by Edward Edelson entitled "BUCKYBALL--The Magic Molecule", published in Popular Science, August 1991, a good review of the discovery, methods of production and uses of fullerenes or "buckyballs" is made. An article by Robert F. Curl and Richard E. Smalley entitled "Fullerenes" in Scientific American for October 1991 discusses the difficulties encountered in producing "visible amounts" of fullerenes and describes the carbon arc method for making the product in microscopic quantities. Another good description in particular of C.sub.60 fullerenes is provided in Chemical Reviews 1991 of the American Chemical Society by Kroto et al., pp 1213-1235, which, among other things describes the isolation, separation and structure characterization of the most useful fullerenes--C.sub.60 and C.sub.70.
Currently the most interesting uses of bulk C.sub.60 and C.sub.70 fullerenes are in electronics, where in various compound forms they can act as an insulator, a battery, a conductor, a semiconductor or a superconductor. Also fullerenes offer interesting opportunities in the plastic and pharmaceutical industries, although their use has been rather restricted until now because of the difficulty to produce them in sufficiently large quantities and at a reasonable price.